In modern electrical power distribution systems, a primary voltage leaves a sub-station and ends as a secondary voltage entering a customer's meter socket. A variety of methods, materials, and equipment are used among various utility companies, but the end result is similar.
Initially, a voltage (i.e. energy) leaves a sub-station in a primary circuit, usually in three phases (though it is possible to send it in a single or dual phase as well). The most common type of primary is known as a wye configuration (so named because of the visual similarity to the letter “Y”.) The wye configuration includes 3 phases (represented by the three outer parts of the “Y”) and a neutral (represented by the centre of the “Y”.) The neutral is grounded both at the substation and at every power pole. In a typical 12470Y/7200 volt system, a pole mount transformer has a primary winding (coil) rated for 7200 volts and is connected across one phase of power and the neutral. The primary and secondary (low voltage) neutrals are bonded (connected) together to provide a path to blow a primary fuse if any fault occurs that allows the primary voltage to enter the secondary lines.
An older and less common method of primary configuration is known as delta, so named for the shape of the Greek letter (a triangle). Delta has three phases and no neutral. In a delta configuration there is only a single voltage between two phases (phase to phase), while in a wye configuration there are two voltages between two phases and between a phase and neutral (phase to neutral).
Electric distribution substations transform electrical power from a primary transmission voltage (i.e. a high voltage) to a lower (secondary) voltage used for local distribution to homes and businesses. Losses of power in a cable (or winding) are proportional to the square of the current, the length of the cable, and material resistivity, and are inversely proportional to cross-sectional area.
The main function of distribution transformers is to reduce voltage to the appropriate level required by users. The basic technology behind distribution transformers has not changed appreciably (if at all) over the past 80 years. In most cases, utility companies install and own/maintain distribution transformers. Utility companies size transformers (i.e. determine the required transformer coil size (winding)) based on predicted demand load as provided by a customer. These predictions almost always err on the side of caution and therefore overstate the required transformer capacity. Higher kilovolt amperage (kVA) capacity over actual use of power results in higher energy losses within the transformer coils.
An example is a transformer installed and fused for 100 kVA based on customer prediction. After three months of actual service, it might be noted that the load never exceeds 50 kVA. Because the transformer is set with a larger coil, the minimum energy required to keep the coil energized is higher than would be required if it were fitted with a smaller coil suitable for 50 kVa. The only way at present to make the transformer (and distribution system) more efficient is to replace the 100 kVA coil with a 50 kVA coil. This is expensive, impractical and inefficient.
Energy losses within transformers can generally be divided into two areas: a) load bearing losses (LBL)—a function of losses due to resistance from the winding material that originate in the coils within each transformer unit; and b) non-load bearing losses (NLBL)—a function of maintaining a transformer unit continually energized, caused by a magnetizing current (producing a continual energy loss).
Attempts to solve these problems of inefficiency and energy loss focus on the use of more efficient building materials, or otherwise focus on alternate sources of energy. Although a power supplier can adjust a power transformer (coil) size based on actual load, this requires replacement of an already installed distribution transformer, and is not cost efficient.
The present invention provides a cost efficient solution to matching transformer size to actual customer need, without requiring more energy efficient building materials or alternate sources of energy (though it is compatible with alternate sources of energy requiring transformation from one voltage to another). The present invention also does not require costly replacement of existing transformers if a customer's load demand unexpectedly increases or decreases.